It is generally recognized that superior cleaning of tableware which includes dishes, flatware, glasses, cups, mugs and the like are more reliably or consistently cleaned and sanitized by dishwasher machines than can be accomplished by hand. The principle reasons for this advantage that dishwasher machines have over hand washing is in the use of stronger detergents and considerably higher wash water temperatures at least during the wash and rinse cycles. In the industrial environment, the significant labor cost in any establishment requiring the cleaning of tableware places increased demand on the use of dishwasher machines. There is also considerable use of such machines in most households in view of the better cleaning performance of dishwasher and also because less time is spent in cleaning the tableware.
Institutional dishwashing machines are operated under very demanding conditions. The machines normally operate with a one to two minute cycle during which the dishes are washed and rinsed and ready for reuse. Highly caustic dishwasher detergents are used to obtain meaningful cleaning within that time. In addition, it is also necessary to use various rinse aids during the rinse cycle in order to reduce spotting on the glassware. In the larger institutional dishwashers, electronically controlled pumps may be used for dispensing, from outside the dishwasher through conduits to inside the dishwasher, the necessary quantities of dishwasher detergent and rinse aids. Such electronically controlled dispenser systems are fairly expensive and can only be used in an economical manner on larger institutional dishwasher equipment. Although they work very well in this environment they do require periodic service and attention to ensure that the correct amount of dishwasher detergent, whether it be in liquid or slurried form, and rinse aid are properly dispensed within the dishwasher. By virtue of the dispenser being outside the machine, the dishwasher has to be provided with conduits which extends through the dishwasher tub to permit dispensing of the desired chemicals to within the machine. As a result in accordance with some regulatory laws, various types of fittings are required in the line to prevent mixing of wash liquids with fresh chemicals, solutions, detergents and rinse aids to be introduced to the machine. All of this adds to the complexity, cost and periodic servicing required. However, in view of the large volume of tableware handled by institutional machines, these costs are relatively negligible compared to the overall effectiveness in washing large volumes of tableware.
In other types of commercial establishments which have less demand for tableware washing, a variety of under the counter or above the counter dishwashers are used. Normally these dishwashers have a single rack of dishes which is inserted into the machine, washed for one or two minute cycles and withdrawn for re-use. With such low volume or low end industrial dishwashers, the use of electronically controlled detergent and rinse aid dispensing machines is not cost effective. In the past, for such low end dishwasher machines powdered detergents with or without rinse aids have been used. However, due to the highly caustic nature of the powders, operators of the machines often receive caustic burns and secondly do not always pay the necessary attention to ensure that the correct amount of detergent powder is included in the machine for each cycle. A further difficulty with the use of powders is the slow dissolution rate during the relatively short cleaning cycle. Furthermore, powders do not lend themselves to automatic dispensing within the dishwasher.
Powdered dishwasher detergents also present a problem from the standpoint of incorporation of rinse aids. The major problem in incorporating rinse aids in highly caustic industrial type dishwasher detergents, is that the rinse aid is not stable in the caustic composition, so that the effectiveness of the rinse aid is lost during storage and before use. Hence in most situations a separate rinse aid is used in conjunction with powdered dishwasher detergents.
Liquid dishwasher detergents are best suited for use particularly for industrial type dishwashers because of their ready dispersability in the dishwasher water and their relative ease of dispensing. Liquid dishwashing detergents are therefore commonly used in the larger capacity dishwasher machines because they may be readily pumped to within the dishwasher. As already mentioned however, the electronically controlled pumping systems for dishwasher detergent liquids are not cost effective with low end type dishwashing machines. Furthermore, to retrofit any type of external dispensing device requires drilling the cabinet and dishwasher tub to provide for installation of dispenser conduits to within the dishwasher.
A further difficulty with the use of liquid dishwasher detergents is that bulk supply of the liquid can present problems in filling reservoirs either positioned within the machine or on the exterior thereof. Spillage of the very caustic materials presents a considerable hazard to the operator as well as to surrounding equipment.
Although there are various types of dispensers available for dispensing powder into dishwasher machines, in view of the presence of moisture and heat in the dishwasher, the powder dispenser has to be of a design which avoids caking of the powders and subsequent malfunctioning of the equipment. For example, the powder dispensing device of U.S. Pat. No. 2,500,059 could not operate in the hot moist environment within a dishwashing machine. Similarly, the more complex electronic system of U.S. Pat. No. 4,875,607, although it would function adequately outside of a washing machine, could not function within the dishwashing machine because of the moist, hot environment. As to the dispensing of liquids to within the machine as already explained, there are the complex electronically controlled pump systems. However, there does not appear to be available in the marketplace any type of liquid dispensing device which operates consistently and may be positioned within the dishwasher.